Electrostatic coating apparatus



June 29, 1948. RANSBURG 2,444,144

ELECTROSTATIC COATING APPARATUS Filed June 16, 1944 mvsu'ron M 1179M): G

I IDW/ BY 4 M flrr Patented June 29, 1948 ELECTROSTATIC COATINGAPPARATUS Edwin M. Ransburg, Indianapolis, Ind., assignor,

by mesne assignments, to Ransburg Electro- Coating Corp, Indianapolis,Ind., a corporation of Indiana Application June 16, 1944, Seriallilo.546,648

14 Claims.

This invention relates to an apparatus for coating articles in anelectrostatic field wherein said articles are first dipped in a bath ofcoating material and then passed through an electrostatic field forremoving excess coating and tear drops, reference being had to LettersPatent No. 2,359,476, granted on an application of Charles K. Gravley,October 3, 1944, entitled Electrostatic method and apparatus.

In the application of paint, lacquer or other coating materials by thedip process, the excess material which invariably remains at thedrainoil point after substantial flow has ceased, has always been a,problem which has seriously limited wide spread application of this mosteflicient coating method. The accumulations which remain at the drainoff points are referred to as tears." In accordance with theabovepatent, a process and apparatus is disclosed which accomplishes theremoval of this excess material and leaves the finish on the articlesmooth and complete. This removal is accomplished by so arrangin theapparatus as to cause the dipped articles to pass at the correct timethrough an electrostatic field, wherein an electric force is applied toall parts of the article which tends to pull it toward a spacedelectrode charged at high voltage. If the article is rigidly held andthe excess coating material is suffi-ciently liquid, it will be pulledofi of the article, leaving a coating that is smooth and free from teardrops or similar excess material. This removal of excess material isherein referred to as detearing.

Heretofore the attractin high, voltage electrode has been spaced to oneside of the article. However, it has been found advantageous in applyingthis method to numerous articles to place the electrode below thearticle so as to combine the attractive force of the electrode with theforce of gravity. This arrangement, however, immediately gives rise todifficulties in that the drippings build up and accumulate on theelectrode in repeated use of the'process, such as ocours in large scaleproduction. Although the build-up of the material on. the electrode doesnot aflect its electrostatic efficiency, it becomes unsightly and notgood practice, and involves considerable effort and loss of time inperiodically cleaning and removing its accumulation of drippings.However, more important, if the accumulation of the leading edge of theelectrode becomes excessive, and if the material remains liquid for anylength of time, it will have a tendency to re-detear back onto thefinished work.

It is, therefore, one of the objects of this invention to provide meansfor materially reducing the build-up of coating on the electrode and there-detearing thereof back onto the work. In any electrostatic detearingoperation the detearing action will always take place from points,edges, or sections of small radius. Because electrodes, as usedheretofore, have been designed with a relatively sharp leading edge,material which accumulates on this edge will, if it remains fluid,eventually present an excess which may be deteared back on to the work.In order to prevent this action, the leading edge of the electrode, inthe present invention, is attached to a downwardly curved smoothsurfaced apron of a radius which is relatively large compared to thework being treated.

Another feature of the invention resides in the" provision of a driptank extending under the apron into which the liquid or drippings aredirected, said drippings being carried away by a constant flow of waterin the drip tank. Said drip tank may also be utilized to carry away andtrostatic forces to detear excess material from the detearing electrode.

The full nature of the invention will be understood from theaccompanying drawing and the following description and claims.

The drawing is a perspective view of the apparatus illustrating theinvention. In the drawing there is shown an overhead conveyor track IIIfor continuously conveying a group of articles II to be coated. Saidarticles are, for purpose of illustration, herein shown as shell casesto which a coating of varnish is to be applied. The articles are carriedin groups bya supporting hanger l2 carried by a suitable conveyor alongthe track I 0.

A dip tank I3 is provided for containing a bath of coating material Itinto which the articles are submerged and removed by a dip in theoverhead conveyor track l0, said articles being moved in the pathindicated by the arrows. Spaced from the dip tank along the line oftravel of the articles there is provided an underlying electrode llsupported in spaced hori ontal relation'to the line of travel of theartic es so that the articles are caused to pass thereover followingtheir travel through a predetermined space between the leading edge ofthe electrode and the dip tank.

A source of high voltage indicated at i6 has one terminal thereofgrounded and the other terminal connected to the electrode l by the leadwire ii. The overhead track is grounded and is electrically connectedwith the articles through the hangers l2. Thus, the articles aregrounded to one side of the source of high voltage and the electrode I5is at a high potential in respect thereto, suchas to create anelectrostatic field therebetween. The resultant fleld thus establishedcauses an increased force, over that of gravity, on the residualdroplets or excess coating, such as to draw them from the articles. Thisaction takes place as the articles approach the leading edge of theelectrode, and hence the major portion of the excess material anddroplets is withdrawn from the articles toward said leading edge.

To prevent a build-up of the removed coating material on the leadingedge of the electrode, such as may cause a re-detearlng action or firehazard, a drip apron i8 is provided. Said drip apron comprises theleading edge of the electrode, that portion thereof which receives thegreater amount of removed'material. To prevent the material building upon the drip apron, it is provided with a smooth downwardly curvedsurface, such as to cause the liquid material to rapidly 'draintherefrom as it is received and thereby prevent it from building up.Upon draining by gravity to the lower edge IBA of the apron, thematerial will then detear to the drip tank I9 which is the moreconvenient of the two adjacent grounded objects, rather than back to thecoated articles. This rounded surface also isdesigned so that itpresents a surface of sufficiently large radius to preclude detearing ofthe wet material back onto the work. The balance of the electrode may bein the form of a large mesh screen, as illustrated.

Below the plane of the electrode l5 and extending along the path oftravel of the articles from the dip tank to. the electrode, there isprovided a drip tank l9 containing a water bath which flows through saidtank from an inlet pipe 20 teen outlet pipe 2|. By means of this driptank spanning the space through which the articles travel beforereaching the apron of the electrode, provision is made for receiving andcarrying away the intermediate drippings, as well as the dripping fromthe apron.

From the foregoing it will be apparent by means of this apparatus thatthe electrostatic force may be combined with the force of gravity towithdraw downwardlythe excess material from, the articles. This is madepossible by the disposition of the electrode, its structure and theprovision for draining its leading edge- The invention claimed is:

1. Apparatus for coating articles comprising means for applying a liquidcoating material to the surface thereof, means operable to convey saidarticles through space to permit drainage of said coating by force ofgravity, a horizontally disposed electrode mounted to extend below andin spaced relation to the path of travel of said articles, means forproviding an electrostatic force be-, tween said articles and saidelectrode capable of establishing an electric force exerted in the samedirection as the force of gravity and in addition thereto for drawingexcess liquid coating material downwardly from said articles, and adownwardly curved drip apron extending along the leading'edge of saidelectrode to initially receive said withdrawn excess of material andpermit it to freely flow therefrom.

2. Apparatus for coating articles comprising a dip tank containing abath of coating material, a conveyor operable to submerge said articlesin said bath and thereafter convey them beyond said tank, a horizontallydisposed electrode spaced from said tank extending below and in spacedrelation to the path of travel of said articles. means for providing anelectrostatic force between said electrode and articles capable ofdrawing excess liquid coating material downwardly therefrom, and adownwardly curved drip apron extending along the leading edge of saidelectrode for initially receiving said excess material and provide adraining medium therefor.

3. Apparatus for coating articles comprising a. dip tank containing abath of coating material, a conveyor operable to submerge said articlesin said bath and thereafter convey them beyond said tank, a horizontallydisposed electrode spaced from said tank extending below and in spacedrelation to the path .of travel of'said articles. means for providing anelectrostatic force between said electrode and articles capable of drawing excess liquid coating material downwardly therefrom, and a watercontaining drip tank extending between said dip tank and electrode forreceiving and disposing of excess coating drawn from said articlesduring their passage therebetween.

4. Apparatus for coating articles comprising a dip tank containing abath of coating material,

. a conveyor operable to submerge said articles in said bath andthereafter convey them beyond said tank, a horizontally disposedelectrode spaced from said tank extending below and in spaced relationto the path of travel of said articles, means for providing anelectrostatic force between said electrode and articles capable ofdrawing excess liquid coating material downwardly therefrom, adownwardly curved drip apron' extending along the leading edge of saidelectrode for initially receiving said excess material and provide adraining medium therefor, and a water containing drip tank extendingbetween said dip tank and electrode for receiving and disposing ofexcess liquid drawn from said articles during their passage therebetweenand from said apron. I

5. Apparatus for coating the surface of an article comprising means forapplying a liquid coating to said surface, means operable to support thecoated article in spaced relation to a receiver positioned to receiveexcess coating material therefrom, a detearing electrode located betweensaid article and receiver, said electrode having a curved surfacepresented toward said article and terminating in an edge portionpresented toward said.

receiver, and means for creating a high potential difference betweensaid electrode and article and between said electrode and receiver,whereby excess material will be deteared' from the article to saidelectrode and from said electrode to the receiver.

6. Apparatus for removing excess liquid coating material from an articlecomprising means for conveying the article through space to permitdraining of said excess material, a detearing electrode extendingadjacent to butspaced from the tion of said electrode being curved in aradius greater than the radius of that portion of the article from whichcoating material is deteared,

and means for establishing an electrostatic field between said articleand said electrode for removing excess liquid coating material from saidarticle.

8. Apparatus for removing excess liquid coating material from an articlecomprising means for conveying the article through space to permitdraining of said excess material, a detearing electrode extendingadjacent to but spaced from 'the path of article-travel, a portion ofsaid electrode being located below the lowest extremity of the articleand extending away from such path,'and means for establishing anelectrostatic field between said article and electrode. ,1

9. Apparatus for coating an article comprising means for applying aliquid coating to the surface thereof, means for conveying the coatedarticle over a predetermined path to permit draining of excess coatingmaterial from it, a detearing electrode mounted in spaced relation tosuch path, a

receiver disposed below said electrode to receive excess material whichhas left the article, and means for maintaining a-high potentialdifference between said electrode and article and between said electrodeand receiver, said electrode being so arranged relative to said receiverand article that the electrical forces therebetween will combine withthe forces of gravity to detear accumuportion of which is curved awayfrom such path,

and means for establishing between said article and said electrode anelectrostatic field to move excess material from electrode. v y

11. Apparatus for removing excess liquid masaid article to saiddetearing terial from the surface of an articlemcmprising means forconveying said article along a prede- 6 .7 termined path to permitdraining of said excess material, a receiver arranged below said meansto receive excess material which has left the article, means forremoving the material from the surface of said receiver, a detear-ingelectrode placed beneath said path and above said receiver, and means toelectrostatically charge said electrode to a high potential with respectto said article and said receiver.

12. In a coating apparatus, means for applying an excess of liquidcoating material to an article, a detearing electrode spaced from saidmeans, a conveyor for conveying an article over a predetermined pathextending through said coating means and above said electrode, areceiver disposed beneath the path of article travel and between saidcoating means and electrode to receive coating material draining fromthe article, said receiver extending beneath at least the leading edgeof said electrode, and means for electrically charging said electrode tocreate electrostatic fields between the electrode and article andbetween the electrode and receiver.

.13. In electrostatic detearing apparatus, a detearing electrode havinga portion which slopes generally downwardly to an edge, a support for ran article to be deteared, a receiver beneath said Number Name Date309,343 Glaeser Dec. 16, 1884 725,679 Dare .Apr. 21, 1903 1,042,914 Hey]Oct. 29, 1912 1,092,761 Tyler Apr. 7, 1914 2,1? 3,032 Wintermute Sent..12. 1939 2,173,078 Meston Sept. 12, 1939 2,247,968 Ransburg et al July1, 1941' 2,359,476 Gravley Oct. 3, 1944 edge, and means for maintaininga potential difference between said electrode and an article on saidsupport and between said electrode and said receiver, whereby excesscoating material on saidarticle will be deteared to said electrode andcoatconveying the article over said electrode. and said' downwardlysloping electrode portion being at the leading edge of the electrode.

EDWIN M. RANSBURG.

REFERENCES crran The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

